This invention relates generally to a yarn sensor and, more particularly, to a sensor which detects breakage of a moving strand of yarn and produces an electrical signal indicative of such breakage.
Yarn sensors of the invention may be used in conjunction with textile apparatus of the type having a creel and a warp drawing machine. In apparatus of this type, several (e.g., as many as 2500) individual yarn packages are supported by spindles of the creel. Strands of yarn are unwound from and pulled off of the individual packages by the rotatable beam of the warp drawing machine and are wound on the beam to form a warp sheet. Guide means confine each strand for movement along a predetermined path as the strand travels at very high speed from the yarn package to the beam.
If one of the strands breaks, it is necessary to stop rotation of the beam of the warp drawing machine as quickly as possible in order to simplify repair of the warp sheet being formed on the beam. In the past, mechanical switches such as drop wires have been used to detect yarn breakage and to produce an electrical signal effecting stopping of the beam. The drop wire rests on the moving strand and effects closure of switch contacts when the strand breaks. Drop wires require time-consuming threading of the strands through small eyes, have a relatively slow response time and require that the yarn be maintained under relatively high tension in order to prevent the switches from producing false signals and causing frequent "nuisance" stops.
Another type of yarn detector is an electronic motion detector which senses the "ballooning" movement of the yarn as the yarn is unwound from the package. In order for such a motion detector to function, the yarn must be moving in a looping path as the yarn passes the detector. Motion detectors of this type also have a relatively slow response time, require substantial floor space and, in order to prevent nuisance stops, can be activated only after the yarn has achieved relatively high speed (e.g., 400 yards per minute) and developed the proper "ballooning" motion. Thus, such detectors are not effective to detect breakage when the yarn is first starting to move during acceleration of the warper beam and when breakage is most likely to occur.